The following discussion of the prior art is intended to place the invention in an appropriate technical context and enable its advantages to be more fully appreciated. However, any references to prior art throughout this specification should not be construed as an express or implied admission that such art is widely known or common general knowledge in the relevant field.
Various techniques are known for irrigating agricultural crops. One common form involves the use of linear or rotary sprinklers or sprayers. These systems are designed to spray water from a pressurised supply through spray heads of various types into the air in the form of droplets. The droplets then fall to the ground relatively uniformly to irrigate the crops. These “blanket spraying” systems can distribute irrigation water over large areas. However, the distribution is substantially untargeted and as a result, the process is relatively inefficient and the resultant water consumption is relatively high.
Drip irrigation systems are also known, whereby irrigation water is allowed to drip into the soil through fixed networks of pipes, valves, tubes and emitters positioned in the general vicinity of the crops. These systems can be somewhat more targeted in the application of irrigation liquids and fertilisers and can reduce water consumption to some extent. However, the infrastructure is costly to install and maintain, and water consumption on commercial scale agriculture is still relatively high.
Both sprinkler and drip irrigation systems are sometimes used to deploy fertilisers, pesticides and similar chemicals intended to either promote the growth of the target crops or impede the growth of weeds, pests or diseases. Again, however, because these application systems are relatively untargeted, large quantities of fertilisers or pesticides are required and a significant proportion is inevitably wasted.
In an attempt to ameliorate these problems, other techniques such as tractor-drawn sprayers, aerial application spraying (“crop dusting”), and even semi-automated techniques using unmanned aerial vehicles (UAVs) have been used. In all such cases, however, the targeting is at best approximate, with significant quantities of over-spray of costly agricultural chemicals being inevitably dispersed as either airborne droplets, or liquid run-off, with minimal impact.
In many circumstances, using any of these known delivery mechanisms, only a proportion of the irrigation water, or chemical fertiliser or pesticide, is delivered precisely where needed. Aside from the significant cost resulting from this wastage, the environmental effects may be negative, for example if potentially toxic airborne pesticides are inadvertently blown into populated areas under adverse wind conditions, or if chemical run-off works its way into river systems or water supplies. These considerations in turn impose limitations on the types and quantities of agricultural chemicals that can be used.
In an attempt to ameliorate some of these problems, techniques have been proposed whereby a more concentrated jet of water or other liquid is shot more directly at the target plants. However, the nozzles of such systems are usually fixed in position, as a consequence of which the water or other liquid can only be dispensed at a point in time when the nozzle is oriented correctly toward the target. In other words, there is only a single solution to the targeting problem. In an attempt to overcome this limitation and increase the resolution of such systems, it has also been known to include a number of independently operable outlet nozzles along the length of an extended boom or spray bar. However, this significantly increases cost, size, weight and complexity of the apparatus. These factors also render the system impractical in many mobile applications, particularly airborne vehicular applications.
It is an object of the present invention to overcome or ameliorate one or more disadvantages of the prior art, or at least to provide a useful alternative.